二、第一个Mybatis程序
思路:搭建环境-->导入Mybatis-->编写代码-->测试
2.1搭建环境
搭建数据库
create database `mybatis`;
use `mybatis`;
create table `user`(
`id` int (20) not null PRIMARY key,
`name` VARCHAR(30) DEFAULT null,
`pwd` VARCHAR(30) DEFAULT null
)ENGINE=INNODB DEFAULT CHARSET=utf8;
select * from user;
insert into `user` (`id`,`name`,`pwd`) VALUES
(1,'酱油','123456'),
(2,'张三','123456'),
(3,'李四','123456')
新建项目
1.新建一个普通的maven项目
2.删除src目录
3.导入maven依赖
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.jiang</groupId>
<artifactId>Mybatis-Study</artifactId>
<version>1.0-SNAPSHOT</version>
<!--导入依赖-->
<dependencies>
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.46</version>
</dependency>
<!--mybatis-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
</project>
2.2创建一个模块
编写mybatis的核心配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置文件-->
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
</configuration>
编写mybatis工具类
package com.jiang.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
//sqlSessionFactory -->sqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static{
try {
//使用Mybatis第一步:获取sqlSessionFactory对象
String resource="mybatis-config.xml";
InputStream inputStream = null;
inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
//既然有了SqlSessionFactory,顾名思义,我们就可以从中获得SqlSession的实例了
//SqlSession完全包含了面向数据库执行SQL命令所需的所有方法
public static SqlSession getSqlSesssion(){
SqlSession sqlSession = sqlSessionFactory.openSession();
return sqlSession;
}
}
2.3、编写代码
实体类
package com.jiang.pojo;
import lombok.Data;
import lombok.RequiredArgsConstructor;
@Data
@RequiredArgsConstructor
public class user {
private int id;
private String name;
private String pwd;
}
Dao接口
package com.jiang.dao;
import com.jiang.pojo.User;
import java.util.List;
public interface UserDao {
List<User> getUserList();
}
接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.jiang.dao.UserDao">
<!--id为dao/mapper层内函数的名字,resultType返回结果-->
<select id="getUserList" resultType="com.jiang.pojo.User">
select * from mybatis.user;
</select>
</mapper>
2.4、测试
MapperRegistry是什么?
核心配置文件中注册mappers
<!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册-->
<mappers>
<mapper resource="com/jiang/dao/UserMapper.xml"></mapper>
</mappers>
Junit测试
package com.jiang.dao;
import com.jiang.pojo.User;
import com.jiang.util.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
@Test
public void test(){
//第一步:获得SqlSession对象
SqlSession sqlSesssion = MybatisUtils.getSqlSesssion();
//执行SQL
//方式一:getMapper
UserDao userDao = sqlSesssion.getMapper(UserDao.class);
List<User> userList = userDao.getUserList();
//方式二:
List<User> userList = sqlSesssion.selectList("com.jiang.dao.UserDao.getUserList");
for (User user:userList) {
System.out.println(user);
}
//关闭SqlSession
sqlSesssion.close();
}
}
可能会遇到的问题
1.配置文件没有注册
2.绑定接口错误
3.方法名不对
4.返回类型不对
5.Maven导出资源问题
https://www.bilibili.com/video/BV1NE411Q7Nx?p=3&spm_id_from=pageDriver